Oracle has released the Linux base install repositories to the public. This means that, when you have obtained the ISOs for OEL4 or OEL5, you can install packages freely using yum. The so-called "base channels" are available for free and without support over Internet. This applies to Oracle VM (Xen) as well. All you need is their .repo files, yum check-update, and you're set.
Updates and Patches require a support license. Check Oracle Public Yum Server for details and howto.
Comments
yum check-update
I get ...
Reading repository metadata in from local files
No Packages marked for Update/Obsoletion
Which is strange because I know there should be several updates available...
What could I have done wrong?
Perhaps, try 'yum clean all' first and then a 'yum check-update'. Also, your server may need a proxy to access Oracle's public yum channels. Use '$ export http_proxy=http://your_proxy:port/' to define a proxy before doing the yum update.
(Sorry for the late reply)